1. Field of the Invention
The present invention relates generally to an internal combustion engine of the type wherein coolant is "boiled off" to make use of the latent heat of evaporation of the coolant and the coolant vapor used as a heat transfer medium, and more specifically to an improved coolant level control arrangement therefor.
2. Description of the Prior Art
In currently used "water cooled" internal combustion engines, the engine coolant (liquid) is forcefully circulated by a water pump through a circuit including the engine coolant jacket and a radiator (usually fan cooled). However, in this type of system a drawback is encountered in that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat. Further, due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having 1800 cc displacement (by way of example) is operated at full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this a flow rate of 167 l/min (viz., 4000-60.times.1/4) must be produced by the water pump. This of course undesirably consumes a number of horsepower.
In order to overcome this problem it has been proposed to "boil" the coolant and use the vaporized coolant as a heat transfer medium thus taking advantage of the latent heat of evaporation of the coolant. Examples of such arrangements are found in U.S. Pat. No. 1,376,086 issued on Apr. 25, 1921 in the name of Fairman and in European Patent Application Publication No. 0059423 published on Sept. 8, 1982.
However, with such arrangements a problem has been encountered that it is difficult to maintain an adequate level of coolant in the coolant jacket and to avoid either overfilling or underfilling of same especially in automotive applications wherein the attitude of the coolant level changes with change in orientation of the engine and/or vehicle and/or under the influence of centrifugal force when the vehicle traverses a corner or the like. A further problem has been encountered in that upon boiling of the coolant extraordinarily large gas bubbles are sometimes produced which displace the coolant from a particular portion of the coolant jacket permitting the formation of "hot spots" therein. These so called "hot spots" due to their inherent elevated temperature tend to promote the formation of further large gas bubbles which subsequently induces a localized "dry out" within the coolant chamber. This of course leads to knocking and/or thermal damage (e.g. piston seizure).